The present invention generally relates to the detection and localization of a leaking tube from among a plurality of such tubes. While the concept embodied in the invention is generally applicable for detecting leaks within any system having tubes extending across an enclosed chamber, it is particularly well suited for detecting leaks in condenser tubes forming part of a steam condenser.
By way of background, steam is utilized in many power generating systems to drive turbines. Such systems comprise a boiler, the turbine itself, and a condenser which are all interconnected into a single closed-loop system. The boiler is used to produce steam which is, in turn, circulated to the turbine for driving same. The spent steam, together with condensate formed as a result of passage through the turbine, is then circulated through the condenser wherein the steam component thereof condenses back to water. The water exiting the condenser is next returned to the boiler where it is converted into steam and then recirculated to again drive the turbine.
Power generating systems of the kind just described typically utilize a condenser which includes a large plurality of condenser tubes, in the order of several thousand, extending between and supported by a spaced pair of plates or sheets (hereinafter referred to as tube sheets). All such condenser tubes are positioned within an enclosed condensation chamber which receives the combined steam and water from the turbine. The tube sheets themselves form part of the wall structure of the condensation chamber and the condenser tubes are connected to the tube sheets in a manner rendering them accessible at their opposite ends from the outside of the condensation chamber.
Cooling of the steam to convert it to water is facilitated by circulating cooling water through the condenser tubes. This typically involves withdrawing water from an adjacent lake or river, communicating the water through one end of the condenser tubes, and then discharging the water from out the opposite end of the tubes back into the lake or river. Because such sources of cooling water typically contain suspended and dissolved solids and other contaminants in admixture therewith, it is necessary to ensure against cooling water intrusion into the closed-loop system to thereby alleviate corrosion and other like problems. Intrusion of cooling water may occur if one of the condenser tubes develops a leak along a portion located within the condensation chamber. Similarly, a leak developing along the seam between the tube sheet and the condensation chamber may also result in cooling water intrusion. By virtue of the vacuum produced in the chamber as a result of the condensation process, certain of the cooling water may be drawn through the leaks and thereby contaminate the closed-loop system water used to produce steam.
Heretofore, all methods for detecting and locating leaks in condenser tubes have required shutting down and removing off-line at least a portion of the power generating system, thereby resulting in the loss of energy capacity. While many present-day systems employ a plurality of condensers therein, in some of those systems the removal of even only one condenser from on-line operation requires shut down of the entire system.
In addition to the resultant loss of energy producing capacity, the prior art methods also suffer from the drawbacks that they are difficult to carry out, time consuming to perform, and, in most instances, require the presence of personnel within the inhospitable environment of the condenser itself in order to locate leaks.
One such prior art method is disclosed in Pelletier et al., U.S. Pat. No. 4,226,113, issued Oct. 7, 1980. Briefly, that patent discloses a method for detecting condenser tube leaks wherein the condenser is first removed off-line and then individual groups of condenser tubes are treated for leaks by directing therein a discrete amount of tracer gas such as, for example, helium. In practicing the method, suitable pump means are connected to one end of the condenser tubes to create a vacuum therein and thereby cause the tracer gas to flow through the tubes. If one of the tubes within the group of tubes being tested has a leak, a portion of the tracer gas will escape from the tube through the leak into the condensation chamber. Suitable means are provided for sampling the atmosphere within the condensation chamber surrounding the tubes to detect the presence therein of any tracer gas which may have been leaked.
A variant form of the Pelletier et al. method is disclosed in Frei, U.S. Pat. No. 3,425,264, issued Feb. 4, 1969. In the Frei method the condenser is removed off-line and both the condensation chamber and the condenser tubes are cleared of process fluids. Thereafter, suitable pump means are utilized to evacuate the tubes to a pressure lower than the chamber pressure, and simultaneous therewith a tracer gas is injected into the chamber. If a leak is present in any of the condenser tubes the leaking tube will draw in the tracer gas and subsequent sampling of each of the tubes will reveal which, if any, of them are leaking.
Another method for detecting leaking tubes is disclosed in Brachet, U.S. Pat. No. 3,975,943, issued Aug. 24, 1976. Briefly, Brachet discloses a method for detecting steam and/or water leakage from circulation tubes surrounded by an alkaline molten metal. More specifically, the apparatus to which the method is applied is a heat-exchanger including a plurality of circulation tubes having water and/or steam flowing therethrough. The circulation tubes are arranged in predetermined groups whereby each group of circulation tubes is separately enclosed between a spaced pair of baffles forming a compartment or channel through which liquid sodium flows. With the heat exchanger on-line and in full operation, the liquid exiting all of the channels is monitored for the presence of water, indicative of a leaking tube. In the event that the presence of water is detected, then various groups of circulation tubes are successively removed off-line, drained of water and/or steam, and then pressurized with an inert gas. Assuming that the group of tubes removed off-line contains the leaking tube, then sampling of the liquid sodium would reveal the absence of water, and, therefore, it would be known that the leaking tube was among the group then being held off-line. The tube from that group actually leaking is then determined by bringing the entire apparatus back on-line, and then individually sampling the liquid sodium flowing through each channel which has one of the tubes from the group positioned therein to thereby locate which of the tubes is leaking. While the Brachet method represents an improvement over the other methods previously discussed in that it permits the majority of the heat-exchanger to remain on-line during the carrying out of the method, it too nevertheless suffers from the drawback that at least some of the apparatus must be taken off-line in order that the leaking tube may be detected. Furthermore, it will be readily appreciated that Brachet is generally limited to apparatus having only a few tubes as compared to the several thousand typically present in a steam condenser. The Brachet method also suffers from the additional drawback that it is incapable of detecting a leaking tube in the case where the fluid flowing through the tubes and through the channels is of the same chemical composition.
In view of the foregoing drawbacks residing in the prior art, it is the primary object of this invention to provide an improved leak detection system and method which enables power plant personnel to quickly and accurately locate one or more leaking tubes without having to remove any part of the power plant off-line.
Another object of this invention is to provide a leak detection system which is both rugged and durable, as well as being both easy and inexpensive to operate and maintain.
A still further object of this invention is to provide a leak detection system and method which only minimally, if at all, interferes with the normal operation of a power generating system, and to the greatest extent practicable is compatible with such power generating systems to thereby alleviate the possibility of damage to the system such as may be caused by galvanic corrosion and other like deleterious phenomena.
It is also an object of this invention, that, once the leaking tube(s) has been located, the subsequent occlusion of that tube can be performed rapidly and efficiently with only minimal off-line time for the power generating system.
It is also an object of this invention to provide a leak detection system which is capable of operation despite the disposition thereof within cooling water having comtaminants admixed therewith, which contaminants might otherwise adversely effect the leak detection system reliability.
Another object of this invention is to provide a leak detection system and method which utilizes normal fluid flow through condenser tubes, or the like, and a condensation chamber, or the like, to carry detectable tracer fluid.
Yet another object of this invention is to provide both a leak detection system and method which uses a gas as the tracer fluid, and which is both accurate and reliable regardless of the orientation of the condenser tubes.